I hadn't thought about rack pulls, I think the temptation'd be too much to load them up heavy as hell. .
Yeah, I've known some lifters who do rack pulls strictly as an upper back thickener. In my case, I was a tall, skinny runner with a gimpy back who was trying to get into cross training. The problem - beside the backache - was that I sucked at lifts like squats and bench presses because of my long limbs. But a trainer at the gym told me that I would be a natural for deadlifting, and he was right. He put me on the rack pull -> trap bar -> deadlift progression to ease my fears about throwing out my back
I'm thinking with the RDLs I'll be more likely to be slow and controlled, and can get a good stretch in the hamstrings which might help towards addressing my woeful flexibility
True. But for traditional deadlifts with heavier weights, you don't want to be slow at the start - you'll have trouble getting off the floor. Slow training with the RDL might not carry over well.
But we all have to learn by doing.